Electric motors, such as brushless motors, may be used for many different applications. In many instances, analog Hall-effect sensors are used for sensing rotor position in brushless motors where, for example, trapezoidal commutation is employed. This can be a cost effective solution when precision motor control is not needed. However, for precision motor (e.g., fine resolution) control applications, which employ sinusoidal or field oriented control commutation, relatively higher resolution position and rate sensing may be needed. Historically, this higher resolution sensing has been accomplished with relatively more expensive and complex resolver type AC sensors and resolver to digital conversion circuitry.
Recently, other techniques have been implemented that use relatively low-cost analog Hall-effect sensors. In accordance with these techniques, analog Hall-effect sensors generate three sinusoidal signals representative of the position of the motor rotor. Using a rigorous mathematical approach, the rotor position and rate may then be derived. One example of a mathematical approach, which is disclosed in U.S. Pat. No. 6,744,230, combines the three sinusoidal signals into two orthogonal vectors using known trigonometric identities. Standard arctangent algorithms and other trigonometric identities may then be used to derive the rotational position and rate from the orthogonal vectors.
While the above described mathematical technique works quite well, it can exhibit certain drawbacks. For example, the derived position and rate can be subject to a number of errors. These errors may be associated with individual Hall-effect sensors or specific magnet poles. In particular, the Hall-effect sensor errors may arise from positioning errors (phase and amplitude) and/or from electrical offset of the sensors. The magnet pole errors may appear as overall magnetic flux intensity variations or distortions in the sinusoidal waveform.
Hence, there is a need for a relatively low-cost motor control scheme that may implement fine resolution motor control and that overcomes inherent sensor errors and rotor magnetic flux intensity variation errors. The present invention addresses at least this need.